Situation:Citrus
peelminer has been reported mining the peel of citrus fruits in the southwestern
U.S. since the early part of the twentieth century. The earliest known
collection from a mined orange peel collected 23 July 1915 from Pasadena,
California. The peelminer is considered to be native leafminer normally
attacking willow, which has undergone a host shift to various non-native
plants including citrus and oleander. On citrus, larvae almost always
attack the fruit and rarely infest leaves.

Damage: Larvae of peelminer
form serpentine mines on the fruit of citrus. Grapefruit, lemon and lime
are most susceptible to damage but the peelminer attacks all varieties,
as well as stems of oleander, avocado fruit, stems of cotton and leaves,
and stems of willow. Under heavy infestations, peelminer will mine the
leaves of citrus, but this is rare. Mines are serpentine and lack any
associated frass line. Eggs are laid directly on fruit. Pupation occurs
outside the mine in cracks or crevices in the tree within silken cocoons
ornamented with small spheres. Peelminer has a short developmental time
and as many as 6-13 generations per year can occur.

Economic Impact: Citrus
peelminer causes direct damage to the peel of grapefruit, and although
damage is cosmetic, as few as 2-3 mines per fruit can render fruit unacceptable
for the fresh market. In 1995, a severe infestation in the Coachella Valley
resulted in the loss of 80-90% of grapefruit in some groves. The peel
of the fruit can become completely mined and take on an overall blistered
appearance.

Distribution: Citruspeelminer has been reported as an economic pest in California,
Arizona and Cuba, although it has been noted (but never accurately identified
and may be another species) in low numbers in Texas and Florida. The peelminer
is found throughout southern California as far north as Tulare County,
but only appears to be a sporadic pest in desert regions.

Distribution by County

Control: One native gregarious
eulophid wasp, Cirrospilus coachellae, provides good to excellent
control of peelminer populations. The parasite pupates in the mine and
can be seen through the epidermis as a series of small naked black pupae
surrounded by black dots (fecal pillars). Often, several exit holes surround
the remains of pupae. More than one generation of parasites is produced
for each host generation and from 2-7 parasitoids develop on each host
killed, allowing for rapid expansion of the parasite population. In average
years, peelminer populations are highest during summer months when fruit
are growing, with numbers declining and parasitism increasing to 60-90%
by late August. Applications of pesticides have not been a successful
control strategy. Peelminer is active through winter, but parasitism remains
high. The cultural practice of removing all
mined fruit from trees 3-4 weeks before new fruit is set in spring is
the best means of reducing outbreak populations of the moth in the following
year.

Cirrospilus pupae in mine

Print version originally prepared by the
Citrus Research Board, California Department of Food and Agriculture and
the University of California Exotic Pest Management Center. Photographs
courtesy of Marta Guillen and Eldon Reeves.